personal cycle forecast · Generated Your 6-month forecast
Predicted period days, fertile window and ovulation — based on your average cycle.
Upcoming important dates — next 12 cycles
What counts as an irregular cycle?
Cycles are usually called irregular when they vary by more than about 7–9 days from one cycle to the next, or when they are consistently shorter than 21 days or longer than 35 days. By that definition, research summarized by the NICHD suggests 14% to 25% of women have irregular menstrual cycles — you are far from alone.
Common drivers include stress, significant weight change, intense exercise, illness, coming off hormonal birth control, the years after giving birth, perimenopause, and conditions such as PCOS or thyroid imbalance.
How range prediction works
Instead of pretending to know your exact cycle length, this calculator asks for your shortest and longest typical cycles. Your next period is then predicted as a window: earliest = last period + shortest cycle, latest = last period + longest cycle. Ovulation and fertile windows are shown as ranges too, each anchored 14 days before the possible period dates.
You will notice the ranges widen for cycles further in the future. That is not a flaw in the tool — uncertainty genuinely compounds over time, and showing it honestly is the whole point.
Making your ranges narrower
The single best upgrade is data: log each period start here for three to six cycles. Your personal shortest/longest (and your average, in regular mode) become real measurements instead of memories, and predictions tighten accordingly.
It also helps to note disruptive weeks — illness, travel, extreme stress — when they happen, so an outlier cycle does not distort your ranges.
When irregular cycles deserve a doctor visit
Irregularity is common and often benign, but some patterns merit evaluation: cycles consistently under 21 or over 35 days, no period for three or more months (with pregnancy ruled out), soaking through a pad or tampon every hour, bleeding longer than seven days, or severe pain. These can point to PCOS, thyroid disease or other treatable conditions.
How it works
Enter your last period
Pick the first day of your most recent period — the day full bleeding started, not spotting.
Set your cycle length
Not sure? Use the built-in helper: enter a few past start dates and we compute your personal average.
Get instant answers
Next period date, ovulation day, fertile window and a 6-month forecast — plus a heads-up if you're running late.
Log it, and it gets personal
When your period actually starts, come back and tap "Log this period". After two or three logs we learn your real cycle length — not the textbook 28 days — and your predictions start using it.
Frequently asked questions
Is there a period calculator for irregular periods?
Yes — this one. Enter your shortest and longest typical cycle lengths and you get predicted date ranges for your next periods, ovulation and fertile window, instead of a single date that would pretend your cycles are regular.
How do I calculate my next period with irregular cycles?
Use your shortest cycle for the earliest possible date and your longest cycle for the latest. For example, with a last period on August 1 and cycles of 26–32 days, expect your next period between August 27 and September 2.
Can I get pregnant with irregular periods?
Yes. Irregular cycles usually still ovulate — the challenge is timing. A fertile-window range like the one this calculator shows is especially useful, and tracking several cycles improves it.
Why are my cycles irregular?
Frequent causes are stress, weight change, intense exercise, illness, hormonal birth control changes, postpartum and breastfeeding, perimenopause, PCOS and thyroid imbalance. New or worsening irregularity is worth discussing with a clinician.
When should I see a doctor about irregular periods?
If cycles are consistently shorter than 21 or longer than 35 days, vary by more than 9 days, you miss three or more periods, or you have very heavy bleeding or severe pain, book an evaluation.
Does irregular mean infertile?
No. Irregular cycles mainly make ovulation harder to predict, not impossible. Many people with irregular cycles conceive; tracking ranges and symptoms — and talking to a clinician when trying — helps.